Streaming music services have brought big changes to the music industry. But one important part of the business has not kept up: Billboard's album chart.

Now Billboard and Nielsen SoundScan, the agency that supplies its data, will start adding streams and downloads of tracks to the formula behind the Billboard 200, which, since 1956 has functioned as the music world's weekly scorecard. Silvio Pietroluongo, Billboard's director of charts, said that by looking at streams as well as sales, the new chart will more accurately reflect how people listen to music these days.

"We were always limited to the initial impulse, when somebody purchased an album," Pietroluongo said. "Now we have the ability to look at that engagement and gauge the popularity of an album over time."

Changing habits

One expected result is that albums by big pop stars — which tend to open high on the chart and then plunge after just a few weeks — should linger longer in the upper rungs. For example, Ariana Grande's "My Everything," which opened at No. 1 in September, was No. 36 by mid-November. Under the new formula, it would have been No. 9.

SoundScan and Billboard will count 1,500 song streams from services like Spotify, Beats Music, Rdio, Rhapsody and Google Play as equivalent to an album sale. For the first time, they also will count "track equivalent albums" — a common industry yardstick of 10 downloads of individual tracks — as part of the formula for album rankings.

The change is being welcomed by record companies that have been frustrated with the old chart's blind spots. Daniel Glass, the founder of Glassnote Records, an independent label whose acts include Mumford & Sons and Chvrches, said that Billboard's charts play a vital role in the industry by demonstrating the success of a new act. These days the fans of those acts may stream more albums than they buy.

"It's been very difficult over the last two or three years to communicate the charts to radio stations," Glass said. "I've been Scotch taping and Band-Aiding Shazam and Spotify, bringing in all this data for them. Now with this all-in-one streaming chart, it's a much truer reflection of how much is being consumed."

Album sales in the first half of the year declined 15 percent from the same period in 2013, according to SoundScan. But streaming from on-demand services like Spotify — which let people pick what songs to listen to, unlike radio services — was up 42 percent in the same period.

"Album sales have become a smaller and smaller part of the industry," said David Bakula, a senior analyst at Nielsen. "To just look at album sales and say this is how we measure success is really leaving out that half of the business that is coming from streams and song sales."

Winners and losers

With each tweak Billboard makes to its charts, there is often a corresponding uproar. Last year, Billboard began counting YouTube views for the Hot 100, its pop singles chart. Critics worried at the time that the practice would reward novelty viral videos, and indeed the first beneficiary of the change was Baauer's "Harlem Shake," a song with modest sales but huge exposure through dance-along videos online.

This change might hurt artists whose albums are not on streaming services or mostly consumed through sales. Barbra Streisand's "Partners," for example, would drop from No. 7 to No. 13 under the new rules.

But Taylor Swift's "1989," the biggest hit album of the year, was withheld from streaming outlets and still shot up to No. 1 on the charts.

"No amount of streaming in the world could keep Taylor from No. 1," Bakula said.